Viscosity indicating and controlling apparatus



May 20, 1952 w. M. TRIGG 2,597,138

VISOSITYA INDICATING AND CONTROLLING APPARATUS Filed July 5l; 1947 2SHEETS--SHEET l INVENTOR Warren M. Trigg @u grandi MM WITNESSES:

May 20 1952 w. M. TRIGG 2,597,138

I -VISCOSITY INDICATING AND CONTROLLING APPARATUS l Filed July s1, 19472 SHEETS- SHEET 2 WITNESSES: INVENTOR Wan/? A/l. Trigg. QM@

Patented May 20, 1952 VISCSITY INDICATING AND CONTROLLING APPARATUSApplication July 31, 1947, Serial No. 765,232

7 Claims.

This invention relates to the regulation or control of viscosity offluids and more particularly to apparatus for automatically controllingas well as indicating the viscosity of a fluid.

In many industrial processes, there is involved some fluid material andin many cases the vis- ,cosity of the fluid is an importantcharacteristic bearing on its suitability for such application.Viscosity has been dened as the resistance to flow in a liquid. Often itis necessary to control the viscosity of a fluid within some relativelynarrow range in order to secure best results. For example, the viscosityof coating compositions determines the thickness of the coating whichmay be applied under a given set of conditions. Viscosity may alsocontrol the ease with which a given surface is covered. In wireenameling, for example, the thickness and the uniformity of coating isclosely related to the viscosity of the enamel being applied. Thethickness of an enameled coating on enameled wire must be maintainedwithin certain narrow limits if the wire is to meet standardspecifications. Many uid compositions such as oils, paints, resinsolutions, waxes, polishes, and the like must be prepared Within apredetermined range of viscosity before use or sale to the trade. In allthese and in mam other cases, the viscosity must be known as well as becontrolled within close limits.

While a variety of laboratory devices is available for the purpose ofdetermining viscosity, tests performed therewith are often timeconsuming and not readily adaptable for control of viscosity since thereis no provision for directly controlling the viscosity of the fluidbeing tested by any known laboratory devices. VAttempts have been madein one or two known instances for automatically controlling theviscosity of a fluid by means of suitable equipment. However, experienceshows that these devices are not sufficiently reliable or accurate toenable close control. Such rknown apparatus has been found to beextremely costly and the results do not justify such costs. Further,constant check-up with laboratory instruments is required to maintainthem in operating condition. Therefore, the common practice is to usemanual control based on laboratory instrument tests.

The object of this invention is to provide an automatic viscositycontrol device, responsive to minute changes in viscosity of the fluidbeing controlled.

A further object of this invention is to provide a device capable ofcontrolling the viscosity of a fluid to a precise value by addingthereto a viscosity modifying component. v

A still further object of the invention is to provide an apparatus forcombining materials in such proportions as to attain a predeterminedviscosity value. f

Other objects of the invention will in part be obvious and will in partappear hereinafter.

For a fuller understanding of the nature and objects of this invention,reference should be had to the following detailed description anddrawings, in which:

Figure l is a view in elevation, partly in section of one embodiment ofthe invention;

Fig. 2 is a fragmentary view partly in sectionv of another modificationof the invention, and

Fig. 3 is a fragmentary View of a third embodiment of the invention,partly in section.

According to the present invention, a portion of a fluid whose viscosityis to be measured, and regulated or controlled by adding thereto aviscosity modifying component is pumped at constant volume and atconstant temperature through a conduit of such dimensions that asignificant drop of pressure is present between the ends of the conduit.The pressure drop Ap in a conduit is given by K L met# where u is theabsolute viscosity L is the length of the conduit u is the averagevelocity of the fluid d is the diameter of the conduit.

With a conduit of fixed length and diameter, and when the uid is pumpedat a constant volume so that the average velocity is constant, thepressure drop Ap is directly proportional to the viscosity. This drop inpressure has been employed to operate a suitable mechanism to controlthe viscosity by introducing the viscosity modifying component. Inpractice, it has been found advantageous to magnify the pressure dropbetween the ends of the conduit by means of suitable relays, switchesand power mechanisms to operate a valve or a pump, as well as to effecta record of the viscosity.

Referring to Fig. 1 of the drawings, there is illustrated -an apparatuswhich is suitable. for precisely controlling or maintaining theviscosity of a fluid, such as a Wire enamel, by adding thereto solventin such proportions as to thin the wire enamel to a predeterminedviscosity. The device is particularly suitable for treating wire enamelbeing withdrawn from enameling towers or the like where a substantialportion of the solvent may have evaporated under the influence of heat.The wire enamel is recirculated to the Wire enameling towers continuallyin order that thinner or solvent may be added thereto to maintain aprecise degree of viscosity to enabledeposition of a coating of enamelof the required thickness in wire.

1n the channel Ii a portion .of Wire enamel II which is uniformly ofhigher viscosity than desired for enameling is drawn into the conduit I2Where it is heated in a heating device I4 tov a predeterminedtemperature as set on a thermostat I5. Since viscosity is a directfunction of temperature, it is quite critical that-the Atemperature bemaintained substantially constant, usually within 1 C. or less.

The temperature employed may be set at any suitable Value. It has beenfound that a temperature value of 120 F. is excellent for'wire enamel.Since it is wellabove room temperature it can be secured at all times.and maintained .accurately; Heavy oils may` be heated higher, to say160 F. or more, to reduce their absolute viscosity.

andtested Without any changein the apparatus. Depending on therequirements, ,the latitude of permissible temperature variation maybeless or morethan this value. A constant volume pump I6, for example, agear pumpora multiple` piston pump, forces the enamel into: a conduit|534 small p that detection of small.: changes will; be difficult andthe degree of controlthat mayvr be derived therefrom `will becorrespondinglyless precise. A conduit of extremely Iinediameter may besubject to considerableerratic.V variations in pressure drop and forthis reason may not be too suitable. Ihavetfound that a ratio of lengthto diameter of a circular cross-section conduit in the range of to 500is suitable.

for use with most liquids of a viscosity of from 0.2 to 5,000centipoises. Heavier liquids,- such as certain heavy oils, asphalts andthelike will require eithermore heat to -electY a viscosity reduction ora proportionate change -in -theconduit dimensions, usually to a largerdiameter,v so as to give pressure drop values suitableforeasymeasurement. l

The input end of the conduit I8 comprises a T4 2I|=toWhich'is-connected` the pipe 32 provided with arvalve` 24and Ythe outputendof the conduit comprises another T 22 to which lis` fixed ai secondpipe 34 provided with a valve 26.- An equalizing pipe with the valve-28connects the pipes 32 and 34. Valve 28 lis closed except when pipe-30 isbeing employedfor the purpose-of setting zero viscosityor pressure dropconditions. The pipes 32 and 34 areconnected to al pressure-responsivedevice 36--within which is amovable .piston 38, or .'othenmovable.partitioni member which may be a' diaphragm orthe like.` A spring 40applied to the upper orlow: pressure side ofthe piston Sil-may`beadjusted by the setting screwv 4I to anyY predetermined setting.

If the., diameter of the pipe iszexcessive, the, pressure drop will belso` i A piston rod 42 attached to piston 38 extends from the device 35and is moved in response to the changes in pressure on the faces of thepiston.

It will be apparent that when a fluid of relatively high viscosity ispumped through the conduit I8-, the pressure in pipe 32 will beincreased with respect to the pressure in pipe 34, whereby the piston 38will move upward. Upon decrease in vviscosity in a iiuid passing throughconduit I8, the pressure difference between 32 and 3ft will diminish andthe piston 38 will tend to move downwardly. By adjusting the screw si,the position of the piston 6E and the rod 52 may be-ad-justed inaccordance with the Viscosity of a Yfluid being circulated through theconduit I5. The setting of screw di will control viscosity and it may beprovided with a pointer and a fixed scale to indicate settings.

The end of the piston rod @l2 remote from piston.38.moves within acontrol valve mechanism 4d where the piston rod carries a slide valve i6capable of closely iitting the Walls of the cylinder 48 and normallycovering a port leadingY to a pipe 58. Compressed air at substantiallyconstantpressure from a reservoir 50 or other supply source enters by aninlet 52 to the portion A ber 54 which exhausts to the atmospherethrough the exhaust outlet 56. Upon movement of the slidevalve deupwardly in response to an increase in pressure drop in the conduit It,compressed air. in` the cylinder i8 will be admitted to the pipe58 bythe port exposed by such movement ofthe slide valve. Increased airpressure in the pipe-58. is conveyed by a feedback line Sii to achamber-62 in control valve mechanism te where it operates on'a pistonEil fastened to the end ofthe connecting rod 42 thereby tending toreturn the slide'Valve 4S to the position where it closes the portleading to pipe 5d. Correspondingly, .when the relative pressure drop inconduit I8 decreases, the piston 38 moves downwardfjwhereby the pistonvalve 5c permits air in the pipe 58to` enter the chamber 5d and thusexhaust :tothe atmosphere through outlet 56, and airpressure in chamber62 is simultaneously exhausted throughthe feedback line B sufciently to;permit .the piston valve it to move upwardly and;.close the port leadingto pipe. Therefore,V thereis maintained a ypressure in pipe EGproportionaltd the viscosityof a fluid passing through the conduit I8. Y

Air'in pipe 53- is delivered to a regulator Valve 66 to act 4upwardlyagainst a diaphragm E3 therein., Actingupon the upper side of thediaphragmY 68` is a spring l0. The diaphragm 6s has a valve stern I2attached-thereto for movement in response to movement of the diaphragmin accordance with the air pressure in pipe 58. The valve stem 'I2controls the position of a valve 75 which opens and shuts oif the fiowof thinner or solvent in the pipe vfrom a supply tank 78. The thinnerinpipe 'I5 is under a suitable pressure so that it.will flow readily whenthe Valve 'l is opened. The thinner passes from pipe as a stream 82'into the wire enamel where it mixes in by convection and distributioneffects or by a suitable mixing means (not shown) to produce enamel 88of predetermined viscosity.

The portion 0f wire enamel passing from conduit I8 past the outlet T 22is delivered to a well ibiV ata constant pressure head. The enameldrains'from the well 84 through the overiiow pipe 86; The well 84enables samples of the undiluted enamel I I to be taken. y

The apparatus of Fig. 1 comprises means responsive to changes inviscosity, namely the pressure drop responsive device 36 cooperatingwith a compressed air control valve mechanism 46 which, in eifect, willmagnify the pressure drop in the former to such proportions as tooperate the valve for adding solvent. The ratio of such magnication,everything else being equal, is proportional to the areas of piston 38and piston 54. A ratio of from 5:1 to 100:1 is ordinarily suiicient.

In some cases the pressure drop in conduit i8 may be sufficient tooperate a valve or other suitable mechanism of simpler construction andoperation than in Fig. l. Referring to Fig. 2 of the drawings, there isillustrated a control mechanism of this kind. The pressure responsivemember |00 has connected thereto the high pressure and low pressurepipes 32 and 34 operating as shown in Fig. 1 for effecting relativemovement of a piston |02 in coordination with a spring |04 which isapplied with a predetermined pressure through the set screw |06. Apiston rod |68 moved by piston |02, is connected to the contact arm of aswitch H0. The switch ||0 is adapted to open and close the circuit ||2energized from a sourceof electrical energy H4 which may be a battery, agenerator or the like. The circuit 2 comprises a coil I |6 embodying asolenoid plunger I |8 which reciprocates a valve stem to open and closethe valve |22 disposed in the valve body |24 therebyto control flow ofthinner from the pipe 16 into the pipe 80. A spring |26 pulls thesolenoid |98 and valve |22 downwardly when the coil ||6 is not energizedthereby to close the valve. The electrical switch I l0 may be of suchconstruction as meets the requirements of the application in which theviscosity controlling device is embodied. Thus the switch I I0 maybe aswitch which may be opened or closed by relative movements of a fewhundredths of an inch for securing close control of viscosity or it mayrequire considerable changes in movement of rod |08 before valve |22 isenergized.

It is often desirable to have a mechanism in which a predetermined valueof nuid viscosity may be selected and set and the mechanism will vautomatically follow such set value and operate to produce a fluid ofthe selected viscosity by adding a viscosity modifying component to theuid as required. An apparatus capable of so functioning is illustratedin Fig. 3 of the draw- .1:

ings. There the pipes 32 and 3:3 from the high and low pressure ends ofthe conduit I8, as in Fig. 1, pass iiud into a pressure responsivemember |50 containing a movable piston |52 upon which the adjustablespring |54 acts subject to the position of a set screw |56. A connectingrod |58 attached to the piston |52 moves in response to the movement ofpiston 52 in response to the relative pressure difference on the upperand lower face thereof which, in turn, is dependent on the relativepressures in lines 32 and 34. The connecting rod |58 extends into acontrol valve mechanism |60 wherein a sliding valve |68 is reciprocatedin a cylinder |56 to control the air pressure in line |10. Compressedair via a conduit |12 from a compressed air tank or other source |12enters a chamber I 64 defined between sliding valve |68 and a sealingpiston |69. .Since the air pressure in chamber |62 operates on equalareas on valve |68 and sealing piston 6 |69, changes in compressed airpressure in tank |14 will not aect the operation of the mechanism |60.When the sliding valve |68 is moved upwardly from the positionillustrated in the drawings, air entersthe line |18. Compressed air isvented from the line |10 to chamber |64v and to the atmosphere by anexhaust |16 when the sliding valve |68 is lowered from the positionshown in the drawings. The air pressure in line |10 passes through afeedback pipe |18 to the chamber where it acts on the upper surface ofpiston |82 fixed to the end of rod |58 whereby to center the slidingvalve |66. Therefore, the air pressure in line |10 is proportional tothe viscosity of the iiuid applied tothe apparatus. The compressed airin pipe |10 passes to a cylinder |86 of a first air motor |84 where itacts on and may move a piston |88 and a rod |90 fixed to the piston. Therod |90 is provided with a xed shoulder |82 against which one end of aspring |94 exerts a pressure. A xed abutment |56 restrains the other endof the spring |94. The end |98 of the rod |90 is adapted to applypressure against one arm of a positional member 200 in the form of aT-shaped lever. The other arm of the T-shaped lever member 200 is actedupon by a second air motor 202 comprising a piston 204 operating in acylinder 206 and carrying a piston rod 268. The rod 208 is provided witha fixed shoulder 210 against which a spring 2|2 exerts pressure. The end2|4 of the rod applies pressure tending to move the positional member200 in a direction contrary to that caused by movement of the end |98.

The spring 2|2 abuts against an adjustable t bracket 2|8 aixed to aslidable arm 220 carrying a pointer 222 which may be read or positionedagainst a scale 2|6. The slidable rod 220 is provided with a threadedportion 224 which is engaged by a threaded adjusting nut 226 held fromlateral movement by the fixed stops 228. By rotating the nut 226, theslide member 220 and the bracket 2'8 may be moved horizontally to anydesired point. The pointer 222 indicates the setting of the nut 226. Thescale 2| 6 may be calibrated to indicate viscosity values directly.

Air to operate the second air motor 202 enters throughla pipe 230connected with a valve mechanism 232 in such a way as to receive airfrom an air chamber 234 therein. The valve mechanism 232 carries anexhaust valve 236 maintained in closed position by the spring 238.Counterclockwise movement of positional member 200 causes an arm 241thereon to move upwardly thus opening exhaust valve 236 and permittingair to exhaust from chamber 234 to the atmosphere through an exhaustvent 240. Upon clockwise movement of positional member 200, the arm 241moves downwardly and opens a valve 242, normally maintained in closedposition by a spring 24d, whereby compressed air from a conduit 246 isadmitted to the chamber 234.

The chamber 234 communicates through the pipe 248 with an air pressureoperated valve 250 consisting of a diaphragm 252 directly connected to avalve stem 254 to move a valve 256 to an open or to a closed position.The valve 25e` controls the iiow of thinner from the conduit 15, fedfrom a tank of thinner 13, to an outlet 80 to the body of uid in troughI0. The iiuid 88 with such added thinner thereby is maintained at aselected viscosity.

.The operation of the air motors |84 and 202 in combination with thevalve mechanism 232 is as follows. Assuming an initial neutral positionfor,l all the'. parts .as shown in.Fig,g..3,.upon. an increase ofviscosity; thefluid passing;

through conduit I8, the piston.|52 ismoved upwardly due to arelativeincrease in. pressure in: pipe 32 with respect to the pressure. in pipeA34.

Sliding valve |68 is moved. upwardly by piston |52 and compressed airisadmitted to line: |70 from chamber |62 until enough pressure isbuiltup to f an extent suicient to act on ypiston |82 tocause..

reverse'motion of the rodH |58, thereby causing downward movement ofsliding valve .|88 to closet more air with an increase in pressure isdelivered Due to the pressure incr-ease to chamber 234. in chamber. 234air passesthrough the pipe 238 to the cylinder 26.in the second airmotor 202 thereby applying more force on the piston 204 toV the rightand upon the air pressure in the chamber 234 building up suiicientpressure will be ap-V plied by end 2M to the positional member 260 tomove the piston |88 to the left until the positional member 28|) isreturned to neutral position. The increase in air pressure in chamber234 is transmitted by pipe 248 tothe diaphragm 252 which operates thevalve 25S to permit the iiow of thinner. Such flow of thinner will bemaintained as long as the viscosity is atthe predetermined high level.

If the viscosity of the enamel passing through conduit I8 drops, avproportional decrease in pressure between pipes 32 and 34 will result inthe piston |52 being lowered and sliding valve |88 connecting line |15vto` exhaust chamber |64 whereby the pressure in line |18 and chamber |86is reduced proportionately until such reduced pressure reacting onpiston |82 allows sliding valve |68 to cover the port to line |10.Thecorresponding decrease in pressure in chamber |88 of the first airmotor |84 causes a decrease in thepressure applied to the positionalmember 200 by the end |98 of the rod |98 and, therefore, the arm247iwillbe moved counterclockwise by end 2M of thev secondair motor, therebypushing the valve 238 to open position to exhaust air iromlthe chamber234. The drop -in pressure in chamber 284 is communicated to the chamber2880i the second air motor whereby the pressure on piston28ll dropsuntil the vpositional member Zreturnstoaneutral vposition due tothebalance ofv pressures. applied ends |88 andv 2HE of the first and secondairmotors respectively.

Theoperation ofr the viscosity indicating and controlling device 228,222, 2i6v, etc., is as follows. Assuming'a fluid of agiven viscosity ispresent in conduit i8 and all of the mechanism is in the substantiallyneutral position, when it is desired to secure a'luidY of lowerviscosity, the nut 22S is rotatedso that the bracket 2 8 is moved to theleft to increase the'pressure on the'spring EEE. The increase inpressurein spring2|2 is communicated to the piston rod-288 rthereby un,-balancing the relativeV pressures appliedby ends |98 and 2 I4 to thepositional memberZ whereby the positional memberZll is moved.vclockwise. This results in admitting air under pressure to chamber 234.which operates the'regulator valve 250 and admits a correspondingLincrease oi thinner to the enamel. The secondzairrmotor 282 is aiectedbythe increase in air pressurefin cham.- ber 23ltso as to move theY piston.rod.2|l8due Lto record-of the viscosityof the fluidimay,y be made in`addition to securing a control of the viscosity bythe apparatus.'

While the specific, embodiments .of lthe invention'vin the drawingsWerealldireCted to .the'control of viscosity of an enamel byaddingrthinner thereto, it Wouldbe equallyfeasible. toz'add a heavier.or thickening; constituent, such as resin..

to the enamel if it were desired to increase ther viscosity oftheenamel.: This `wouldonly entail connectingthepipe Eil-to the chamberaboverthev diaphragm 88m the valve 85 in Fig. 1,' orex` ample, andemployingvalve 'I4 to controll the'- ilow of the thickeningVconstituent.. Additionally;

it isLfeasible to control both thefiow of; thinner and thick resin asrequired by` providing a plu:- rality of regulator valves (Fig. l) oneVto'con-r trol the flow of thinner as shown-anda second? one having abranch of the pipe 58 leading. to the chamber above the diaphragm (S8-ina secondzreg: ulator valve to control the owof thick resin; in. Fig. 3,a second regulatorfvalve 258 connected 'to pipe 22S would controlY theflow of theheavier.'

resin. This latter expedient'is particularly suitableV for thecompounding oipaints and other compositions comprising an admiXtureoftwo .or` more components of different viscosity to secure. a compositionhaving a single desired viscosity.

The mechanism oi the present invention.. mayf be employed in combinationwith mixers, blend.- ers, mills, stirrers, and similar apparatus inwhichv ingredients are being combinedtocontrol the addition of one ofthe componentsto the mixerito. reach a predetermined viscosity. Thuspastes,.

adhesives, oils and various fluid preparationsmay be manufactured to aviscosity best suitable. for

use.

In one case, apparatus corresponding in opel-.aeA

tion to thatoi'ig. 3 of the drawings has 'been'.

employed in combination with wire enamelingzr systems. Insuch systems,it hasmaintained the viscosityto so precise a degreethatonly testswithprecisionlaboratory equipment orapparatus` couldi detect` anychanges-.in Viscosity from vthev set value.

Thevalves '#17522 and may be of the full open or full closed type,or'may 13e-proportional opening valvescapableoi regulating the solventow'in any predeterminedv amount between full open and full closedposition. Beth types have been vmade use oiand it has been found thatthey are equally satisfactory;

While the apparatuso img-S. i, 2 and 3 functions to admit solventbyopening a valve, pumpsf may be substituted. Thus in F'g. 2, forexample,l the circuit i l2 may be employed to operate anY electric motorto drive a lpump for adding solvent 'to the enamel. In.Fig. l, the'stem'i2 and'in Fig. 3, thestem 25d would operate a switch to a motor andpump unit. Theuse of amotor driven' pump would be desirable ir" thesolvent were in storagetanks below ground'.

Since certain changes may 'oe-made in the above' invention, anddifferent embodiments of the in; vention may be made without departingfrom thel scope thereof, it is intended that all matter containedfin theabove disclosure or taken in con-V Vnectionlwi-th theaccompanyingdrawings shallbe interpreted as illustrative and not inalimiting sense.

I claim as my invention:

1. An apparatus for controlling the viscosity of a fluid by addingthereto a component capable of modifying the viscosity thereof,comprising, in combination, a substantially constant volume pump forpumping a portion of the fluid at a given temperature, a conduitconnected to the pump output to receive the portion of fluid at constantvelocity therethrough, the conduit being so proportioned that asigniiicant drop in pressure in the fluid is present between the ends ofthe conduit, the end of the conduit opposite the pump being connected tomeans for maintaining a pressure against the outgoing fluid, pressureoperable means connected to both ends of the conduit responsive topredetermined changes in pressure, said pressure operable means beingconnected to a valve means to add the modifying component to the fluid,said pressure operable means including fluid containing pipestransmitting pressure from the outlet and inlet ends of the conduit to asingle enclosed chamber, a movable member disposed within the enclosedchamber to divide the chamber into two compartments, and a spring in onecompartment applying a force to one face of the movable member, the pipefrom the outlet end of the conduit connected to and admitting uid underpressure to one of the compartments whereby the force of the spring andthe outlet pressure unite in acting on the said one face movable memberand the pipe from the inlet end of the conduit connected to andadmitting fluid under pressure to the other compartment to apply apressure on the movable member opposing the force of the spring.

2. An apparatus for controlling the viscosity of a fluid by addingthereto a component capable of modifying the viscosity thereof,comprising, in combination, a substantially constant volume pump forpumping a portion of the fluid, means for maintaining the duid at apredetermined temperature, a conduit connected to the pump outputthrough which said portion of iluid may pass, the conduit being soproportioned that a signicant drop in pressure in the fluid is presentbetween the ends of the conduit, the end of the conduit opposite thepump being connected to means for maintaining a pressure against theoutgoing fluid, pressure operable means connected to both ends of theconduit responsive to predetermined changes in pressure said pressureoperable means being connected to a valve means to add the modifyingcomponent to the luid, said pressure operable means including iiuidcontaining pipes transmitting pressure from the outlet and inlet ends ofthe conduit to a single enclosed chamber, a movable member disposedwithin the enclosed chamber to divide the chamber into two compartments,and a spring in one compartment applying a force to one face of themovable member, the pipe from the outlet end of the conduit connected toand admitting fluid under pressure to one of the compartments wherebythe force of the spring and the outlet pressure unite in acting on thesaid one face movable member and the pipe from the inlet end or" theconduit connected to and admitting iuid under pressure to the othercompartment to apply a pressure on the movable member opposing the forceof the spring.

3. An apparatus for controlling the viscosity of a fluid by addingthereto a component capable of modifying the viscosity thereof,comprising, in combination, a subsantially constant volume l@ pump forpumping a portion of the fluid at a given temperature, a conduitconnected to the pump output through which said portion of fluid maypass, the conduit being so proportioned that a signicant drop inpressure in the fluid is present between the ends of the conduit, theend of the conduit opposite the pump being connected to means formaintaining a pressure against the outgoing fluid, pressure operablemeans connected to both ends of the conduit responsive to predeter minedchanges in pressure, the pressure operable means including iuidcontaining pipes transmitting pressure from the respective ends of theconduit, a movable member connected to the fluid containing pipes andmoving in response to changes of pressure, and power means associatedwith and energized upon a predetermined movement of the movable memberto operate a valve to admit the viscosity modifying component to thefluid.

4. An apparatus for controlling the viscosity of a fluid by addingthereto a component capable of modifying the viscosity thereof,comprising, in combination, a substantially constant volume pump forpumping a portion of the fluid at a given temperature, a conduito-onnected to the pump output through which said portion of fluid maypass, the conduit being so proportioned that a signiiicant drop inpressure in the fluid is present between the ends of the conduit,pressure operable means connected to both ends of the conduit responsiveto predetermined changes in pressure, the pressure operable meansincluding a movable partition, a first valve operated by the movablepartition, the rst valve controlling the ow of compressed fluid tooperate a iiuid pressure regulated valve controlling the iiow of themodifying component to the fluid, and feedback means operated by theflow of compressed fluid to the pressure regulated valve to position thefirst valve to terminate flow of compressed fluid upon a predeterminedfluid pressure being attained for operation of the pressure regulatedvalve.

5. In an apparatus responsive to changes in viscosity of a liquid from apredetermined Value, in combination, a substantially constant volumepump for pumping a portion of the fluid at a given temperature, aconduit connected to the pump output to receive the portion of fluid atsubstantially constant velocity therethrough, the conduit being soproportioned that a significant drop in pressure in the iluid is presentbetween the endsof the conduit, means attached to the output end of theconduit for maintaining a back pressure against the outgoing fluid,iiuid containing pipes connected to each end of the conduit,.the fluidcontaining pipes transmitting pressure from the respective ends of theconduit to a common member comprising a single movable chamber and amember in the chamber responsive to the difference in the pressuretransmitted through the respective fluid containing pipes, one

of the pipes connected to the chamber to apply pressure to one face ofthe movable member and the other pipe connected to the chamber to applypressure to the other face, whereby the movement of the member is inresponse to the higher pressure, and a single compression spring ofregulable force applied to the face of the movable member affected bythe pressure from the outlet end of the conduit whereby the springpressure is added to the outlet pressure on that face to oppose theinlet pressure applied on the other face.

6. The apparatus of claim 1 wherein said pressure operable means isprovided with a means to `operate aneleotricalnswitch,andtazsource'ofeelectrical I energy yand ,anf eleetrically ,operatedvalve controlling flow-of thesmodifying.component; beingv associated-With itheswitch whereby Lthe: addition .ofA modif-ying component* t0'the fluidmaysbe eectedto control ytl1e.viscosity.df the fluid,

-7 The `apparatus :of Claim 1 whereinv the :con-

nection 1 between the pressure .operable Ameans comprises' asourceofpower energizedsin accordance with relative movement, ofthe movablemember to Yap-plypressure rto1a positionable Ymember `controlling yavalve for :.admittingithe modifying component to the uid,1andra secondpressure applying means associated to `apply aan opposing pressure -toYthepositionable member, the :second .1 15

pressure -f applying .means `being adjustable nornInally to enable .a`selected viscosity `for. the fluid to be attained, 'the operation offthe :positionable member beingresponsive to the net'pressure rbetweenthe second pressure applying meansandthe i12. ipower .energized.pressure `means to icontrltfthe valve for adding the modifyingcomponent.

\WARREN M.1TR1GG.

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